The present invention relates to monitoring live electrical equipment at high or medium voltage.
More specifically, the invention relates to monitoring high or medium voltage electrical equipment such as a distribution bay in which the live elements such as the conductors, e.g. busbars or cables, or indeed the insulating parts, are inaccessible, and more particularly the invention relates to monitoring the temperature of such elements.
Conventional practice in monitoring the temperature of live conductors in high or medium voltage equipment consists in taking periodic measurements by means of an infrared camera, and for locations that are inaccessible that requires portholes which are transparent in the infrared. That solution is expensive. Furthermore, it does not provide continuous monitoring. However, it is desirable to be able to monitor the temperature of a set of busbars or other live conductors on a continuous basis so as to be able to detect local overheating and take the necessary preventive measures immediately. Otherwise there is a risk of a thermal runaway phenomenon occurring, and that can have very severe consequences for the equipment.
The use of infrared thermal sensors for continuous monitoring has been studied, but it comes up against difficulties associated with implementation and with the high cost of such components. In addition, those sensors are sensitive to the high electric fields that are produced by the currents being carried by the conductors.
Proposals have been made (Mat Post 99, M 2.3 xe2x80x9cDiagnostic thermique des tableaux MT: une solution xc3xa9conomique et sûre, basxc3xa9e sur un capteur optiquexe2x80x9d [Temperature diagnosis of medium voltage control boards: a solution which is low in cost and reliable, based on an optical sensor] by C. Petit), to use an optical sensor that emits a signal by fluorescence and whose behavior depends on temperature. Nevertheless, that system requires an optical fiber link between the sensor and equipment that includes a light-emitting diode and a photodetector, thereby giving rise to implementation difficulties. In addition, optical fibers are sensitive to mechanical phenomena.
The invention seeks to make it possible to monitor live conductors in high or medium voltage electrical equipment, in a manner that is simple, reliable, and economical.
In accordance with a first aspect of the invention, there is provided a method of monitoring live electrical equipment at high or medium voltage, the method comprising the following steps:
illuminating a zone of the equipment in radio energy close to a point where a physical parameter is to be monitored;
re-emitting the received wave with amplitude-modulation responsive to a digital signal related to said physical parameter; and
receiving the retransmitted wave outside the equipment and demodulating it to obtain a signal related to said parameter.
In appropriate manner, said physical parameter is temperature.
In an appropriate embodiment, said signal is indicative of a threshold being crossed by said parameter.
According to another aspect of the invention, there is provided an apparatus for monitoring high or medium voltage live electrical equipment, the apparatus comprising:
at least one sensor unit placed on the equipment, comprising a first radio antenna, a sensor for producing a digital signal related to a determined physical parameter at a point to be monitored, and amplitude-modulation means connected to the sensor and to the first antenna, and activated by the energy received by said antenna;
a transceiver unit placed outside the equipment and having a second radio antenna for illuminating the first antenna, a power supply source, and signal processing means connected to the second antenna; and
the first antenna retransmitting towards the second antenna the radio wave that has been transmitted thereby, while simultaneously amplitude-modulating it in response to the state of the sensor, said processing means being arranged to provide a signal related to said parameter.